1. Field of the Invention
The invention relates to a dermatologic treatment apparatus and method, and particularly to an apparatus that is light-based, yet eye-safe.
2. Description of the Related Art
The introduction of specialized lasers for physician-performed epilation in 1996 (and intense-pulsed light, or IPL, sources shortly thereafter) represented the first real advance in the treatment of unwanted hair since the invention of electrolysis in the late 1800's. The use of lasers and flashlamps in these devices has not only proven to be safe and effective, but unlike electrolysis allows for the treatment of multiple hairs at a time, greatly improving coverage rate.
Light-based epilation with lasers is often termed “laser hair removal”, although this term is strictly correct only when follicles undergo sufficient thermal damage to permanently prevent the growth of new hairs (“permanent hair reduction”). Procedures that thermally damage follicles to induce a delay in hair regrowth are more accurately described as hair-regrowth inhibition.
Methods and devices for light-based epilation are now widespread and an estimated three million people worldwide have undergone treatment. This represents a very small section of the potential market, largely because of the high cost and inconvenience associated with physician-based procedures and devices. As a result, there is a desire for lower cost, more compact devices that would lower the cost of physician-based treatments and, ultimately, help enable salon and consumer markets. There is also a desire for devices with enhanced eye safety.
The introduction of the LightSheer Diode Laser System by Star Medical in 1997 for hair-regrowth inhibition (and subsequently, for permanent hair reduction) marked the beginning of one of the most successful aesthetic laser applications for the dermatologist's office. With several thousand systems installed worldwide, the safety and efficacy of these and similar devices that followed have been well established. Other such devices include the SLP 1000 (LC 100) diode laser of Palomar Medical Technologies, the Apex 800 diode laser of IRIDEX Corporation, and the F1 diode laser of Opus Medical, Inc.
The radiant exposure applied to the skin (often referred to as “fluence”, expressed in joules per square centimeter) by this class of devices is typically in the 10-40 J/cm2 range at a wavelength of nominally 800 nanometers. It was initially believed that pulse durations in the 5-30 ms range are optimum; however, subsequent studies showed that longer pulses (up to at least several hundred milliseconds) can quite effectively achieve hair-regrowth inhibition, and can also reduce epidermal heating for a given fluence when a heat conduction path is provided (e.g., by incorporating an output window made of sapphire in contact with the skin).
The high efficiency and small size of the semiconductor diode lasers utilized in these devices generally permit the manufacture of compact systems (typically 1-3 cubic feet in volume) and simple 115 VAC operation. However, the systems typically weigh at least 25-100pounds and sell in the range of $40,000 to $90,000. A much lower cost, truly portable device would make this popular procedure much more widely available.
Lasers and intense light sources have gained increasing acceptance among dermatologists for effective treatment of a wide range of applications, such as hair-regrowth inhibition and permanent hair reduction, removal of tattoos, treatment of birthmarks, and facial resurfacing. It is well understood by medical professionals, however, that such light sources are capable of serious eye damage or blindness. To achieve reasonable efficacy with many light-based dermatologic procedures, such as reduction of unwanted hair or destruction of small blood vessels, the fluence on the skin typically exceeds 1 J/cm2. These devices produce a fluence at the human eye that is much greater than the maximum permissible exposure, causing such devices and the treatments performed with them to be extremely hazardous if not used or conducted properly. These procedures therefore involve the undertaking of adequate safety measures to protect the eyes of not only the patient, but the laser operator and any other personnel that may be in the same area. (See, for example, IEC Technical Report 60825-8, Safety of laser products —Guideline for the safe use of medical laser equipment.) As stated in the IEC report, with some medical lasers the retina may be exposed to an irradiance that is more than 100,000 times higher than the irradiance incident on the skin or cornea, due to the focusing action of the eye.
With proper safety precautions, such as safety goggles and training of personnel, the risk of eye damage can be greatly reduced. As a consequence, reports of eye injuries to either patients or staff are rare in medical settings. However, risk of eye injury is a constant concern.
The safety of a light-based dermatologic device can be increased by incorporation of a contact sensor that enables device operation only when in the sensor is in contact with a surface, such as a person's skin. For example, the light source (laser, light-emitting diode, flashlamp, etc.) can be placed within a housing having a single open end through which the light propagates; a contact sensor at this open end can enable operation of the device only if the housing is placed up against a contacted surface. In this manner light can only propagate into or through the surface against which the device is placed. However, use of any type of sensor added to increase eye safety adds complexity and may, of course, fail. Thus, the ideal dermatologic treatment device and method would not depend on electronic circuitry or user compliance with safety eyewear for safe use.
Thus it is highly desirable that any light-based device intended for medical application be designed to minimize possible eye damage for a given level of output fluence or therapeutic benefit, by increasing the inherent eye safety of the light. Existing laser hair reduction devices, for example, are much more hazardous to the eye than necessary because their output is highly directional and easily focused by the eye. If their output could be made more highly divergent and/or to have reduced spatial coherence, there would be a greatly reduced risk of eye injury, without significant loss of efficacy.
Examples of office-based, light-based systems for dermatological treatment are described in U.S. Pat. Nos. 6,508,813, 6,277,111, 6,197,020, 6,096,029, 5,885,273, 5,824,023, and 4,232,678, and U.S. published application no. 2002/0005475, and published PCT application no. WO 03/049633. The '5475 published application uses a contact sensor for enabling laser pulses only when the handpiece is in good contact with a patient's skin. One problem with application of such a device in a home use, self-care setting is that a small child, or person attempting to treat eye lashes or eye brows with the device, may still inadvertently shine pulses into their eyes and potentially cause permanent damage to their vision. Similar eye-safety problems would be apparent in a home use, self-care application of the devices described in each of the above-mentioned patents.
The '49633 published application addresses the eye-safety issue by providing a diffusing unit. However, that device is far too bulky, complex and expensive for home use. The device includes a substantially non-portable laser floor unit and an extensible handpiece connected by a long beam delivery light guide. In addition, other safety issues exist for this device. For example, a home use, self-care setting may not be equipped to handle the electrical safety issues of a device that draws high current from a wall outlet. Most importantly, however, the invention described in the application addresses enhanced eye safety from a collimated laser beam, convergent laser beam, concentrated multiple laser beams or a fiber guided beam, and from monochromatic sources. In contrast, divergent light sources can be rendered eye safe substantially more easily, as described below in accordance with the present invention.
The '029 and '020 patents describe devices that provide fluences over 100 J/cm2. These fluences are generally too large to be eye-safe and epidermis-safe in use in a self-care setting. Such output fluences are likely to give rise to fluences at the cornea potentially above the Maximum Permissible Exposure (MPE), described in more detail below, and/or may likely cause burning of the epidermal region of the treated skin. Moreover, such fluence levels are not efficiently produced in a self-contained apparatus, such as a hand-held and battery-powered device as is desired for self-care and home use in accordance with an embodiment of the present invention.
Furthermore, the device described in the '029 and '020 patents provides a very small spot size between 2 and 5 millimeters in diameter corresponding to approximately 0.03 to 0.2 square centimeters in area. Such a small spot implies that only one hair is treated at a time, and in fact some sort of visual targeting is almost certainly required to ensure that the spot is indeed over even a single target follicle. Also, a small spot size such as between 0.03 and 0.2 square centimeters implies a very low coverage rate. That is, for a given number of square centimeters of skin containing unwanted hairs to be treated, the smaller the spot size the longer the necessary treatment time. In addition, while a small spot size would appear to be quite advantageous in that a low energy can still generate a high fluence on the skin surface (since fluence is energy divided by area), the fluence at some depth within the skin, e.g., where the target cells are located, is substantially reduced by scattering within the skin. That is, the smaller the spot size, especially below about 0.5 cm2, the more pronounced the effective lessening of fluence at depth relative to fluence at the surface. In short, if one goes to too small a spot such as is described in the '029 and '020 patents, the end result can be either burning of the epidermis (to get enough fluence in the dermis) or very poor efficacy due to inadequate fluence at depth; either of these options is obviously undesirable.